How to Databind to a CLR object with Source different to path - wpf

I am trying to update a textblock on the view by databinding to a property in the viewmodel (the datacontext for the view).
In the code below; when SelectedItem changes, I want the textblock text to update with the value of the Name property on SelectedItem.
In an attempt to achieve this I have set the binding source to the property that is changing and the binding path to the data I want to update the textblock with.
I.e. I am expecting that the binding engine will see a change on the binding Source (SelectedItem) and pull the data from the binding Path (SelectedItem.Name).
http://msdn.microsoft.com/en-us/library/ms746695.aspx
Setting the SelectedItem raises INPC but the text does not update.
public class ViewModel
{
public IConfiguration Configuration { get; set;}
}
public class Configuration : IConfiguration, INotifyPropertyChanged
{
public Item SelectedItem
{
get { return _item;}
set
{
_item = value;
ItemName = _item.Name;
RaisePropertyChangedEvent("SelectedItem");
}
}
public string ItemName
{
get { return _itemName;}
set
{
_itemName= value;
RaisePropertyChangedEvent("ItemName");
}
}
}
public class Item
{
public string Name { get; set;}
}
I know that changes on Configuration are seen because this works:
<TextBlock Text="{Binding Configuration.ItemName}"/>
But this does not:
<TextBlock Text="{Binding Path=Name, Source=Configuration.SelectedItem}"/>
And nor does this:
<TextBlock Text="{Binding Path=Configuration.SelectedItem.Name, Source=Configuration.SelectedItem}"/>
I'm assuming that this should be straightforward - what have I missed?

I've never actually seen anyone use Binding.Source before, so I don't know much about it. But my guess is that it's not dynamic. When you create your binding, it's grabbing a reference to the object specified in your Source, and then that's it: it uses that same reference for the lifetime of the binding.
Why make this complicated? Just use Path. That's the normal way of doing binding, and it's dynamic all the way -- what you're doing is exactly what Path is intended for.
<TextBlock Text="{Binding Path=Configuration.SelectedItem.Name}"/>

This is probably working, you just can not see it. The Binding engine has not been notified that the Name property of the Item object has changed.
Try implementing the INotifyPropertyChanged interface on the Item class as well (raising the PropertyChanged event as necessary)
This will work for your third binding situation, and also for a similar definition as below
<TextBlock DataContext="{Binding Path=Configuration.SelectedItem}" Text="{Binding Path=Name}"/>
But for a simpler fix, this should work:
<TextBlock Text="{Binding Path=Configuration.SelectedItem.Name}" />
Edit:
public class Configuration : INotifyPropertyChanged
{
#region INotifyPropertyChanged Members
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
#endregion
private Item _SelectedItem = null;
public Item SelectedItem
{
get
{
return _SelectedItem;
}
set
{
_SelectedItem = value;
OnPropertyChanged("SelectedItem");
}
}
}
public class Item
{
public string Name { get; set; }
}
Then in a Command Execute somewhere I have this:
Configuration.SelectedItem = new Item() { Name = "test" };
Which updates the TextBlock in the View fine:
<TextBlock Text="{Binding Path=Configuration.SelectedItem.Name}" />

Related

WPF - Binding Textbox Text to a class property

I am doing some changes in my WPF project to make it less deprecated.
One of the things I am trying to do is Binding my Textbox.Text value to a simple Class as shown below.
<TextBox x:Name="txtNCM"
Grid.Column="1"
Margin="5"
MaxLength="8"
Text="{Binding Path=Name}"
</TextBox>
public partial class wCad_NCM : UserControl, INotifyPropertyChanged
{
private string name;
public event PropertyChangedEventHandler PropertyChanged;
public string Name
{
get { return name; }
set
{
name = value;
OnPropertyChanged("Name");
}
}
protected void OnPropertyChanged(string name)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(name));
}
}
public wCad_NCM()
{
InitializeComponent();
}
}
Everytime I use the Immediate Window to display the Name's value, it is shown as null. I am really new to this, so I had to search for a similar situation to adapt, but I don't know how to make this work :(
You need to set the DataContext and give Name a value.
To do that, change your constructor to include this:
public wCad_NCM()
{
InitializeComponent();
DataContext = this; // Sets the DataContext
Name = "Test";
}
This should make it work, but is typically bad practice. See http://blog.scottlogic.com/2012/02/06/a-simple-pattern-for-creating-re-useable-usercontrols-in-wpf-silverlight.html for more details.
Additionally, I tried running this and ran into a name hiding problem. Try using a variable name other than Name as FrameworkElement already contains it.

Binding a String to a richtextbox

I have a datagrid populated with "notes" and when a note is clicked I want the richtextbox to show the note.comments. But the Bindings isn't working.
public NoteDTO SelectedNote {get; set;}
public string stringNotes {get; set;}
public void OpenNote()
{
stringNotes = SelectedNote.Comments;
}
<DataGrid x:Name="NoteGrid" cal:Message.Attach="[Event MouseDoubleClick] = [Action OpenNote()]" ItemsSource="{Binding Notes}" SelectedItem="{Binding SelectedNote}"
<toolkit:RichTextBox Text="{Binding stringNotes, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
If I may get help please.
The main problem is that you're binding to a property that has no concept of change notifications; you're not implementing INotifyPropertyChanged. That being said, why not just bind the RichTextBox directly to the property off of NoteDTO:
<toolkit:RichTextBox Text="{Binding SelectedNote.Comments, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
The other option is to manually copy the comments between SelectedNote and stringNotes, then implement INotifyPropertyChanged, but this isn't ideal unless you want to have an intermediate property before propagating them to the NoteDTO object.
EDIT:
I noticed that your SelectedNote property will never notify the UI that it has changed, which will prevent bindings from working. Try something like the following:
public class MyClass : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName)
{
if(this.PropertyChanged != null)
this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
private string selectedNote;
public string SelectedNote
{
get { return this.selectedNote; }
set
{
if (this.selectedNote == value)
return;
this.selectedNote = value;
this.OnPropertyChanged("SelectedNote");
}
}
}

Changing data using ICommand in MVVM

I have two windows: the parent and the child. There is the listbox in a parent window.
MainView:
<Button x:Name="btnUpdate" Content="Update"
Command="{Binding Path=MyCommand}" CommandParameter="{Binding ElementName=lstPerson, Path=SelectedItem}" />
<ListBox x:Name="lstPerson" ItemsSource="{Binding Persons}" />
I'm trying to change selected Person two-way update by using ICommand with parameter.
PersonViewModel:
private ICommand myCommand;
public ICommand MyCommand
{
get
{
if (myCommand == null)
{
myCommand = new RelayCommand<object>(CommandExecute, CanCommandExecute);
}
return myCommand;
}
}
private void CommandExecute(object parameter)
{
var ew = new EditWindow()
{
DataContext =
new EditViewModel()
{
Name = ((Person) parameter).Name,
Address = ((Person) parameter).Address
}
};
ew.Show();
}
But selected instance of Person don't changed in listbox. What do I need to write to the xaml or PersonViewModel to make it working?
P.S.
Here is my Person
public class Person : INotifyPropertyChanged
{
private string name;
private string address;
public event PropertyChangedEventHandler PropertyChanged;
public void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
public string Name
{
get
{
return name;
}
set
{
name = value;
OnPropertyChanged("Name");
}
}
public string Address
{
get
{
return address;
}
set
{
address = value;
OnPropertyChanged("Address");
}
}
}
The parameter of your exceution command for the command is wrong. When your binding to SelectedItem of the list which is bound to an ObservableCollection<PersonViewModel>, the selected item will be of type PersonViewModel. Try initializing the ICommand asRelayCommandand modifyCommandExecute(PersonViewModel person)` accordingly.
Secondly, the ICommand is defined on PersonViewModel, but the Command should be on the ViewModel which holds the Persons collection. So, either you move the Command or you define the command on PersonViewModel in a way that it modifies the particular ViewModel, it is on. Than you can spare the CommandParameter, but bind the command like this:
and make CommandExecute something like this:
private void CommandExecute(object parameter)
{
// Modify this, ie. this.Name = something
}
Last thing, your ViewModel needs to implement INotifyPropertyChanged as well and forward the model change notifications. Otherwise changes will not be reflected, unless the binding to an actual property updates it. For example, if you bind like this
<TextBox Text="{Binding Name, Mode=TwoWay}" />
the Name property on the ViewModel will be updated, but if you call
Name = "ChuckNorris"
in your CommandExecute(..) method, the UI won't be updated, because no change notfication is fired.

How to bind a Property with a textblock From a Class

public class myClass : INotifyPropertyChanged
{
public string myName(string myNameIs)
{
Name = myNameIs;
return myNameIs;
}
public string My = "Hasan";
public string Name {
get { return My; }
set
{
My = value;
OnPropertyChanged("Name");
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged(string propertyName)
{
if (this.PropertyChanged != null)
{
// Raise the PropertyChanged event
this.PropertyChanged( this, new PropertyChangedEventArgs(
propertyName));
}
}
}
.
XAML:
<TextBlock Height="42" Margin="107,245,0,0" TextWrapping="Wrap" Text="{Binding Name}" VerticalAlignment="Top" HorizontalAlignment="Left" Width="159" DataContext="{Binding Source={StaticResource myClassDataSource}}"/>
This is working. But when i update property then it isn`t work?
Your code is rather confusing, you seem to be all over the place with it. I know this isn't the question you asked, but i thought i would point this out anyway:
your member variable is declared as public (public string My = "Hasan";)
your member variable has a totally different name to its property (My and Name)
you have a setter for the public property, and also a setting function (myName(string myNameIs))
you are returning the same value from the setting function as what you passed in
Here is an example of how you could rewrite it:
public class MyClass : INotifyPropertyChanged
{
//normal default constructor
public MyClass()
{
_name = "Hasan";
}
//extra constructor for when you need to set the name to something other than the default
//although this is really only useful if you have no setter on the Name property
public MyClass(string name)
{
_name = name;
}
public string Name
{
get { return _name; }
set
{
_name = value;
OnPropertyChanged("Name");
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged(string propertyName)
{
if (this.PropertyChanged != null)
{
// Raise the PropertyChanged event
this.PropertyChanged(this, new PropertyChangedEventArgs(
propertyName));
}
}
private string _name;
}
You just need to set the TextBlock (or it's parent's) DataContext property to an instance of this class.
Next bind the Text property to the backing property like this
<TextBlock Text="{Binding Name}"/>
Try going through a few tutorials online (or a book) instead of trying to forge your way through. It's easy once you get how DataBinding works.
Update: Once I formatted your question correctly, I could see the XAML you are using...
The mistake here is that you're trying to use the ElementName property (which is used to bind one UI element with another by name). This isn't what you're trying to achieve.

WPF: Nested DependencyProperties

I have an ObservableCollection of "Layouts" and a "SelectedLocation" DependencyProperty on a Window. The SelectedLocation has a property called "Layout", which is an object containing fields like "Name" etc. I'm trying to bind a combobox to the SelectedLayout but it's not working.
The following does not work, I've tried binding to SelectedItem instead to no avail. I believe it may be something to do with the fact that I'm binding to a subProperty of the SelectedLocation DependencyProperty (though this does implement INotifyPropertyChanged.
<ComboBox Grid.Row="2" Grid.Column="0" x:Name="cboLayout" ItemsSource="{Binding Layouts,ElementName=root}" SelectedValue="{Binding SelectedLocation.Layout.LayoutID,ElementName=root}" DisplayMemberPath="{Binding Name}" SelectedValuePath="LayoutID" />
However, the following works (Also bound to the "SelectedLocation" DP:
<TextBox Grid.Row="4" Grid.Column="1" x:Name="txtName" Text="{Binding SelectedLocation.Name,ElementName=root,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" />
What type property Layouts has? I suppose something like this this: IEnumerable<Layout>.
But you bind selected value to Layout.LayoutID. So you got situation, when combo box contains Layout objects, and you try to select it by Int identifier. Of course binding engine can't find any Int there.
I have no idea about details of your code, so one thing I could propose: try to reduce your binding expression: SelectedItem="{Binding SelectedLocation.Layout,ElementName=root}.
If no success, provide more code to help me understand what's going on.
====UPDATE====
As I've said, you are obviously doing something wrong. But I am not paranormalist and couldn't guess the reason of your fail (without your code). If you don't want to share your code, I decided to provide simple example in order to demonstrate that everything works. Have a look at code shown below and tell me what is different in your application.
Class Layout which exposes property LayoutId:
public class Layout
{
public Layout(string id)
{
this.LayoutId = id;
}
public string LayoutId
{
get;
private set;
}
public override string ToString()
{
return string.Format("layout #{0}", this.LayoutId);
}
}
Class SelectionLocation which has nested property Layout:
public class SelectedLocation : INotifyPropertyChanged
{
private Layout _layout;
public Layout Layout
{
get
{
return this._layout;
}
set
{
this._layout = value;
this.OnPropertyChanged("Layout");
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string name)
{
var safeEvent = this.PropertyChanged;
if (safeEvent != null)
{
safeEvent(this, new PropertyChangedEventArgs(name));
}
}
}
And Window class with dependency properties (actually, in my example StartupView is UserControl, but it doesn't matter):
public partial class StartupView : UserControl
{
public StartupView()
{
InitializeComponent();
this.Layouts = new Layout[] { new Layout("AAA"), new Layout("BBB"), new Layout("CCC") };
this.SelectedLocation = new SelectedLocation();
this.SelectedLocation.Layout = this.Layouts.ElementAt(1);
}
public IEnumerable<Layout> Layouts
{
get
{
return (IEnumerable<Layout>)this.GetValue(StartupView.LayoutsProperty);
}
set
{
this.SetValue(StartupView.LayoutsProperty, value);
}
}
public static readonly DependencyProperty LayoutsProperty =
DependencyProperty.Register("Layouts",
typeof(IEnumerable<Layout>),
typeof(StartupView),
new FrameworkPropertyMetadata(null));
public SelectedLocation SelectedLocation
{
get
{
return (SelectedLocation)this.GetValue(StartupView.SelectedLocationProperty);
}
set
{
this.SetValue(StartupView.SelectedLocationProperty, value);
}
}
public static readonly DependencyProperty SelectedLocationProperty =
DependencyProperty.Register("SelectedLocation",
typeof(SelectedLocation),
typeof(StartupView),
new FrameworkPropertyMetadata(null));
}
XAML of StartupView:
<UserControl x:Class="Test.StartupView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:self="clr-namespace:HandyCopy"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Name="Root">
<WrapPanel>
<ComboBox ItemsSource="{Binding Path=Layouts,ElementName=Root}"
SelectedItem="{Binding Path=SelectedLocation.Layout, ElementName=Root}"/>
</WrapPanel>
</UserControl>

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